Dewaxing with evaporative cooling



Patented May 16, 1939 DEWAXING WITH EVAPORATIVE COOLING Edwin C. Knowles, Beacon, N. Y., assignor to The Texas Company, New York,

tion of Delaware N. Y., a corpora- Application Maren s, 1937, serialN. 128,702

4 claims. (c1. 19e-1s) c This invention relates to the dewaxing of mineral oil. Y

In my'co-pending application Serial No. 41,393, there is disclosed and claimed the deWaXing of mineral oil inthepresence of naturally occurring or added wax crystal modifiers, in which'the wax-bearing voil containing such modifier together with solvent is heated to a supersolution temperature which .is substantially above the temperature of complete .Wax solution in order to 'conditionthe Wax bearing oil for wax separation.` 'I'his causes upon chilling precipitation of Wax in a form which gives very substantial incre se in iiltration rates upon filtering the precipitated wax from the oil. 'Ihis mentioned application also discloses the advantage of avoiding substantial mechanical agitation during chilling so as to .avoid objectionable alteration of Wax crystal structure with resultant lowering in filtration rates.

It is an object of the present invention to provide an improvedA method of and apparatus for dewaxing mineral oil, utilizing the features of'v -pending application, and

my above mentioned c; effecting chilling of the`wax-bearing oil in a novel and highly eicient manner while avoiding any substantial mechanical agitation.

It is a further object of the present invention to utilize dewaxing solvents, or solvent mixtures, which are normally liquid at atmospheric temperatures and pressures,- and to obtain partial chilling of the wax-bearing oil by the `flashing of such oil into a high vacuum zone under such conditions that substantial evaporation or distillation of the normally liquid solvent occurs.

It is a further object of the present invention lto provide additional thermal economy in chilling by the use of pre-chilled solvent, preferably solvent which has been recovered by condensation of solvent vapors liberated in' the evaporative cooling of previous chargesof wax-bearing oil.

It is still 'another object of the invention to provide a dewaxing'process of this character enabling a comparatively low solvent dilution ratio to be employed, and to effect substantial thermal economy by a combination of chilling with prechilled solvent and evaporative cooling, with cyclic recirculation of solvent from the evaporative cooling for reuse as additional pre-chilled solvent.

Other objects and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawing and appended claims.

In accordance with the method of the present invention, the Wax-bearing oil to be dewaxed is diluted with a suitable dewaxing solvent or solvent mixture Which is normally liquid at'atmos-` pheric temperatures and pressures. Examples of suitable solvents or solvent mixtures adapted for 5 p use in accordance with the present invention are methyl ethyl ketone and benzol,

Or the oil may contain added wax crystal modi- 20 '.ers of the character ofmontan wax and aluminum stearate, condensation of polymerization l products ysuch as I those obtained by condensation of halogenated waxy hydrocarbons, distillation residues or coal tar and mineral oil products, 25 and other well-known wax crystallization aids of this character. While the invention is particularly described in connection with the use of such a wax crystal modifying material, it is to be understood that features of the invention in- 30 cluding the use of-pre-chilled solvent and evaporative cooling by flash distillation are not confined to the employment of oils containing such Wax crystal modifying materials, but are useful generally in the dewaxing of mineral oil. 35

The oil diluted withv solvent in the ratio of l say 2-3 parts of solvent-'to 1 of oil is heated to a supersolution temperature of the order of about 160 F.-200 F; in order to condition same for Wax crystallization. This oil mix is then shockchil1edas by water-cooled heat exchangers to a temperature of the` order of 10Q-130 F. or somewhat above the temperature of incipient waxv precipitation. This partially cooled oil mix is then vfurther chilled by mixing with a quantity of pre-chilled solvent, thereby raising the dilution ratio at the time of incipient wax precipitation'. For example, the oil mix at "a temperature of around 10U-130 F. may bemixed with an additional quantity ofthe dewaxing solvent at a temperature of about 30-50 F; or' below in the proportion -of Athree volumes of oil mixto one volume of solvent. In thecase where the original wax-bearingoil had been diluted with twov volumes of solvent to one volume of oil, this `tial chilling of the oil mix may be employed inother portions of the chilling range; but this is found particularly useful in lowering the temperature of the oil mix to or somewhat beyond that of incipient wax precipitation, as this has a benecial eiect on wax crystal structure.

The oil mix is then passed through an expansion valve and spray nozzle into a distillation chamber or tower maintained under a high vacuum equivalent to an absolute pressure of about 5-10 mm. mercury or less. Under these conditions a iine spray of the solvent oil mix is formed and a substantial proportion of the solvent will be vaporized with resultant evaporative cooling of the remaining oil mix. This will serve to lower the temperature of the oil mix throughout the greater portion of the range of wax precipitation and thereby accomplish chilling without any substantial mechanical agitation of the type which has been found to be injurious to wax crystal structure. The use of evaporative cooling in conjunction with normally gaseous` solvents has been heretofore suggested, but this requires pressure equipment in which the oil-solvent mix is maintained under high pressure to maintain the solvent in the liquid state, and a portion of the solvent is then allowed to escape or vaporize by release of a portion of the super-atmospheric pressure applied thereto. The present process is distinguished by the employment of normally liquid dewaxing solvents which can be handled throughout the major portion of the equipment in ordinary atmospheric tanks and piping, and by then ashing the oil mix into a zone of high vacuum in the mannerof ash distillation.

Depending upon the character of the solvent employed, the temperature of the oil mix in the ilash distillation vacuum zone may be lowered very substantially, such as to a temperature of the order of 0 F., minus 20 F. or below. The chilling of the oil mix to a filtration temperature of the order of to 20 F. may then be carried out in the customary double pipe 'chiller without objectionable alteration or destruction of the wax crystal structure. By thus chilling the oil through the major portion of the range of wax crystallization without mechanical agitation, it is found that the final chilling to the filtration temperature can be accomplished-in comparatively small sized conventional chilling equipment without substantial reduction in filtration rates of the chilled mix due to alteration in wax crystal structure. The chilled oil mix is then illtered in the usual manner to separate the wax from the oil, as by the use of continuous rotary lters, pressure iilters or filter presses.

The oil filtrate is preferably passed in heat interhange relationship with the solvent vapors released from the nash distillation zone in order to condense the major portin of these vapors. Remaining uncondensed vapors pass to the vacuum producing equipment for the flash distillation zone, and are then discharged through addi- '70 tional condensing equipment, wherein the oil illtrate may be further employed as the cooling medium, to condense the remaining solvent vapors. The recovered solvent condensate at alow temperature is then recycled to the dilution step where the oil mix is diluted lwith pre-chilled soltion is employed; and Fig. 2 is a partial diagrammatic illustrationl of a modification in which a plurality of successive ash distillation stages are employed.

As shown in Fig. 1, the charge of oil-solvent mix is introduced by line l0 to a.steam heater Il where the mix is heated by closed steam coils to a supersolution temperature. `By way of example, the oil may be diluted in a 2:1 dilution ratio with a solvent mixture of 50% methyl ethyl ketone and 50% benzol. The mix is heated to a temperature of the order of 170 F., which is found to condition the oil in the presence of naturally occurring or added wax crystal modifiers for subsequent wax precipitation in a form which materially increases the ltration rate upon separation of the wax from the chilled oil in the subsequent wax filtration step. The heated oil mix is then passed by line I2 through a water or air-cooler i3 where the mix is shock chilled to a temperature of the order of 120 F. The partially chilled mix is then passed by line I 4 to a mixing jet or nozzle I5 into which is introduced additional solvent by line I6. For example, one volume of mixed solvent consisting of 50% methyl ethyl ketone and 50% ,benzol at a temperature of about 40 F. may be added at this point to the three volumes of oil mix coming from the water coolers. Nozzle l5 discharges into an atmospheric tank l1, wherein the diluted oil mix accumulates at a temperature of about F. and in a dilution ratio of three volumes of solvent to one of oil under the conditions set forth above. The oil is thereby chilled by the use of pre-chilled solvent to the temperature of incipient wax precipitation.

The partially chilled mix is then passed by one of branch lines 2 I, 22 and 20 containing shutoff valves 24, 25 and 26 respectively into one of flash distillation chambers or towers 21, 28 or 29. Preferably each flash distillation chamber is constructed as a cylindrical smooth wall tower of substantial height without interior illling or trays. The branch lines 2|, 22 and 20 are provided with expansion valves and spray nozzles 30, 3| and 32 respectively, located just at the point of lntroduction into the top of towers 21, 28 and 29 respectively. The spray nozzles may be arranged to direct the incoming charge in a tangential direction to produce a swirling movement of the nected closed pipe coils 43 through which a heat exchange medium is passed to' eiect condensation of a substantial proportion of the solvent lines 10, 1| and 12 provided vapors. Remaining uncondensed solvent vapor is withdrawn through 42 by vacuum pump 45 and discharged through an additional condenser 46. Solvent condensing in 40 drains into a sump 41 from which it is withdrawn by liquid pump 48 and forced through line 49 to the solvent line I6, so that the solvent is continuously recycled to the chilling system. Remaining solvent condensed in condenser 46 passes by line 50 to line I6. 'I'he condensed solvent may be accumulated in a surge tank 5| from which it is withdrawn to line I6 in order to overcome iiuctuations in the rates of condensation and supply of pre-chilled solvent. An additional chiller for the solvent may be located in line I6, if desired, although this is not necessary in the arrangement shown. The proportioning of oil mix and pre-chilled solvent may be maintained by-suitable proportioning pumps (not shown) in lines l5 and I6 respectively.l

Fiue gas` is supplied to the upper portions of each of the flash distillation chambersfrom a main 55 leading from a source oi supply of flue gas under pressure of about say forty pounds per square inch through lines 56, 51 and 58 equipped with shut-off valves 59, 68 and 6I respectively. Each of the ash distillation chambers is also equipped adjacent the upper portion thereof with a vapor olf-take 63 provided with a shut-off valve 64 leading to a common 'vacuum pump 65 of the flue gas recirculation system, said pump serving to return the ue gas under pressure through line 66 to the gas holder (not shown) which supplies main 55. The towers 21, 28 and 29 are also equipped with liquid discharge with shut-oir valves 13, 14 and 15 respectively, these lines leading to a common line 16 passing through a conventional double pipe chiller 1 where the oil mix is chilled to the nal dewaxing temperature. The chilled mix is then supplied to conventional filtering equipment 18 where the wax is separated from the oil, the wax being discharged at 1,9 and the oil nitrate by line 86. The oil filtrate is forced by pump 8l through line 82 to the connected pipe coils 43 within heat exchanger 40 Where'it is passed in heat exchange relationship with solvent vapors. 'Ihe oil ltrate then passes by line 63. to condenser 46 where it passes in heat exchange relationship with uncondensed solvent va- Dors, and is nally discharged by line 84 leading to conventional stripping equipment not shown.

In operation, the oil mix from tank I1 ispassed to one of the flash distillation towers 21-29. Thus, with the valves 25 and 26 closed and valve 24 open, the oil mix will be passed by line 2| to tower 21, and be flashed through the expansion valve and spray nozzle 38 into the upper portion of the tower. Each ofthe expansion valves and spray nozzles 30-32 is preferably provided with a heating jacket to which hotwater or other heating medium is -supplied to prevent freezing of wax and clogging of the valve and nozzle. Under the conditions mentioned, only valve 36 of the vapor oir-take 33 will be open, valves 31 and 38 being closed. A high vacuum of the order of,

5-10 mm. mercury absolute pressure` will be maintained within the distillation chamber 21. Employing the mentioned methyl ethyl ketonebenzol as the solveht mixture, a temperature of approximately ,10 F. will the iiash tower, and substantially one volume of solvent will vaporize, leaving the oil mixed with unvaporized solvent in the dilution ratio of approximately 2:1.

low temperature are produced chiller be maintained within' As methyl ethyl ketone and benzol boil at substntially the same temperature, the composition of the solvent vapors passing-oli through outlet 33 will be substantially the same as the composition of the liquid solvent remaining in the oil. Where solvents having substantially diierent boiling points are employed, such as methyl ethyl ketoneisopropyl ether, it will be apparent that the solvent vapors will be composed mainly of the lower boiling solvent constituent-in such case mainly of isopropyl ether. It will be readily appreciated that theoriginal dilution of the oil to be dewaxed, and the solvent composition, will be adjusted in accordance with such conditions so as to give the desired proportion of wax antisolvent and oil solvent in the iinal chilled mix passing to the nlters. This can readily be determined for each particular solvent composition. The vapors passing oi through 33 will be largely condensed in the condenser 46 with the result that once the high vacuum and accompanying Within the flash tower 21, this high vacuum and low temperature can be maintained primarily by condensation of the' solvent vapors, and only a small vacuum pump 45 will be r uired in the operation of the system.

When tower '21 has filled to the desired level with oil mix chilled `to the temperature mentioned, valves 24 and -38 will be closed and valves 25 and 31 opened, so that the oil mix will then be flashed into the second flash tower 28. During continuance of the flashing into the tower 28, valve 59 will be opened to supply flue gas under pressure of the order of about forty pounds `per square inch to the top of tower 21, and valve' 13 of discharge pipe 18 will be opened so that the oil mix will be forced by the gas pressure from tower 21 through lines 10 and 16, the double pipe 11 where the mix is further chilled to a dewaxing temperature of the order of F., and then to the filters 18.

Following the lling of tower 28 with oil mix to the desired level and the discharge of chilled oil mix from tower 21 to the filters. valves 26 and '31 will then be closed and valves 25 and 38 opened so that the oil mix is then dashed into the third tower 26. At this time, valves59 and 13 are closed and valves 60 and 14 opened so that the accumulated oil mix in tower 28 is then supplied to the chiller 11 and filters 18. This provides for continuous operation of the iilters. Just before complete emptying of tower 21 of chilled oil mix, and following closing of valves 59 and 13,

valve 64 in line 63 will be opened, so that the large vacuum pump 65 can exhaust tower 21 and produce a high vacuum therein. The vapors so exhausted are returned by pump 65 to the ue gas accumulator in a closed system, so that there is substantially no loss of solvent from the system. During this time, tower 28 is discharging to the lters, and tower 29 is being supplied with fresh oil mix by ash distillation.

At the termination of this portion of thecycle. valves 26, 38 and 64 are closed, and valves 24 and 36 again opened, so that oil mix will be supplied once more to tower 21 by flash distillation. At

this time, the valves areY manipulated so that valve 64 to exhaust gas therefrom and create a high vacuum therein. in the manner stated,

'I'he cycle is then repeated` with one tower operating with flash distillation, a second tower discharging to the filters and the third tower exhausting. Manipulation of the valves may be manually controlled, but is preferably accomplished by synchronizing mechanism from a central station or control board with both manual and automatic controls as is well understood.

The dewaxed filtrate coming from the filter 'I8 at a temperature of around -15 F. is passed by pump 8l through the pipe coils 43 of heat exchanger 40 where it serves to cool and con` dense solvent vapors from the ash distillation tower, while at the same time the filtrate is warmed to a temperature of the order of F. This filtrate then passes through heat exchange coils of condenser 46 where it serves to cool and condense remaining solvent vapors supplied thereto by pump 45. The filtrate at a temperature of the order of 35 F. then passes to the strippers, where solvent is stripped off in the usual manner.

In place of flashing the oil mix into a high vacuum zone for evaporative cooling in a single stage, the process may be carried out in a plurality of series connected ash distillation stages as diagrammatically illustrated in Fig. 2. As

shown therein, the oil mix in the tank Il, corresponding to the tank l1 of Fig. 1, is first expanded through line 86 and expansion valve 81 into a tank 88 which may be maintained under an intermediate vacuum equivalent to an absolute pressure of 60 mm. mercury, by a vapor oiftake 89 containing pressure reducing valve 90 leading to the condensing equipment and vacuum pump as illustrated in Fig. 1. With a solvent mixture of 50% methyl ethyl ketone and 50% benzol, this will produce a temperature of approximately 60 F. in tank 88. The partially chilled oil mix accumulating in tank 88 is discharged through line 9| and expansion valve 92l into tank 93 maintained at an absolute pressure of say 30 mm. mercury by vapor oif-take 95. With the solvent combination mentioned, this will produce a temperature of approximately 35 F. in tank 93. The oil mix accumulating in tank 93 then discharges by line 96 through expansion valve 91` into flash tower 21 maintained at an absolute pressure of about 5-10 mm. mercury by vapor off-take 33 containing shut-off valve 36' and pressure reducing valve 98. Three flash towers corresponding to tower 21 may be provided for the cyclic operation described above in connection with the towers 21-29 of Fig. l. In such case, line 96 will be branched for connection to one or the other ofthe three towers, with suitable shut-off valves in the various branched con- .nections.

The various vapor olf-takes 89, 94 and 33' can be connected to a common condensing and vacuum producing equipment, and the different subatmospheric pressures of the flashing stages can be controlled by proper regulation of the pressure reducing valves 90, 94 and 98. In the caseof some oils, where flashing in a single stage produces too great a turbulence, ebull-ition or foaming in the flash tower, the staged flashing may be employed with advantage.

The present invention oiers the advantages of reduction in solvent ratio, reduction in size of equipment and installation costs, reduction in chilling and stripping costs and reduction in solvent. inventory. The combination of the use of pre-chilled solvent to chill the wax-bearing oil to the temperature of incipient wax precipitation, with evaporative cooling by ash distillation to further chill through the major portion ofthe wax precipitation range, enables the chilling .operation to be carried out in a manner which produces and preserves desired crystal structure, giving high filtration rates, compact wax cakes which are comparatively free from retained or occluded oil, and a high yield of dewaxed oil, while at the same time enabling the dilution ratio of the incoming charge to be maintained at a comparatively low value of the orderof 2:1 or lower.

Obviously many modifications and variations may be made from the present invention without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. In the dewaxing of wax-bearing mineral oil containing naturally-occurring or added wax crystal modifying material, the method comprising diluting the oil containing wax crystal modifying material with a normally liquid dewaxing solvent comprising wax anti-solvent liquid and oil solvent liquid such that the oil and wax are substantially completely dissolved in the solvent mixture at a temperature of about 100 to 130 F., heating the mixture to a temperature of around 160 to l170 F. to condition the mixture for wax separation, cooling the mixture to about the temperature of incipient wax precipitation, atomizing the cooled mixture in a high vacuum zone in the form of dispersed droplets above the normal liquid level therein such that a substantial portion of the solvent vaporizes to provide evaporative cooling of the mixture with resultant precipitation of the bulk of the wax constituents, withdrawing the evaporatively cooled mixture,

-and removing the precipitated wax therefrom.

2. The method according to claim l in which the normally liquid solvent comprises a low molecular weight aliphatic ketone and an aromatic hydrocarbon.

3. In the dewaxing of wax-bearing mineral oil containing naturally-ocurring or added wax crystal modifying material, the method comprising partially diluting the oil containing wax crystal modifying material with a normally liquid dewaxing solvent comprising a wax anti-solvent and an oil solvent such that the oil and wax are substantially completely dissolved in the solvent mixture at a temperature of about 100 to 130 F., heating the mixture to a temperature of around 160 to 170 F. to condition the mixture for wax separation, mixing therewith a further quantity' of prechilled solvent liquid mixture to reduce the temperature of the mixture to about that of incipient wax precipitation, atomizing the resulting mixture in a high vacuum zone in the form of dispersed droplets above the normal liquid level therein such that a substantial portion of 4the solvent vaporizes to provide evaporative cooling of the mixture with resultant precipitation of the bulk of the wax constituents, withdrawing the evaporatively cooled mixture, and removing the precipitated wax therefrom.

4. In the dewaxing of wax-bearing mineral oil containing naturally-occurring or 'added wax crystal modifying material, the method comprising partially diluting the oil containing wax crystal modifying material with a normally liquid dewaxing solvent comprising a wax anti-solvent and an oil solvent such that the oil and wax are substantially completely dissolved in the solvent mixture at a temperature of about 100 to 130 F., heating the mixture to a temperature of around 160 to 170 F. to condition the mixture for wax separation, cooling the heated mixture to a temtherein such that e. perature somewhat above the temperature of solvent vaporizes to provide evaporative cooling incipient wax precipitation, adding' a. further of the mixture with yresultant precipitation of quantity of prechilled solvent liquid mixture to the bulk of the wax constituents, withdrawing chill the wax-bearing mixture to a. temperature the evaporatively cooled mixture, and removing 5 of incipient wax precipitation, atomizing the thus the precipitated wax therefrom.

cooled mixture in a. high vacuum zone in the form of dispersed droplets above the normal liquid level EDWIN C. KNOWLES.

substantial portion of the 

